The present invention relates to an apparatus for and process of hydrolyzing and recycling polyisocyanate derivatives, such as polyurethane resins used in wide applications including furniture, bedding, vehicles, heat insulating materials for building material and consumer electronics, shoe soles and the like, and oligomers of isocyanate compounds in distillation residues discharged in a chemical plant as by-products. Such polyisocyanate derivatives are brought into contact with water heated to high temperature and pressurized to a liquid state, thereby being hydrolyzed and recovered as raw material compounds or derivatives thereof for the target compound. In the present invention, xe2x80x9cpolyisocyanate derivativesxe2x80x9d indicate derivatives having at least one isocyanato group and/or group derived from an isocyanato group, and include wide variety of compounds from low molecular weight compounds to polymers.
In Japan, about 400,000 tons of polyurethane resins are produced in the form of soft, semi-hard, and hard urethane foams, elastomers, and Reaction Injection Moldings (RIM), and are used in various fields. Recently, public awareness of environmental protection have been heightened in all over the world, and under such a situation, studies to develop processes for recycling various kinds of plastics, including polyurethane resins, have been carried out.
Known processes for recycling polyurethane resins are roughly classified in the following categories: 1) a material recycling technique; 2) a chemical recycling technique; and 3) an energy recycling technique. In the material recycling technique 1), polyurethane resins are subjected to a physical treatment such as crushing without changing their physical properties. The crushed polyurethane resins are subjected to thermal press molding or adhesion press molding into new products, or utilized as fillers for extruded products, RIM products, concrete and the like. In the chemical recycling technique 2), polyurethane resins are recovered to raw materials or chemical substances usable as raw materials. Known as chemical recycling techniques are a glycol decomposition method, an amine decomposition method, a hydrolysis method and the like. In the energy recycling method 3), polyurethane resins are utilized as energy resources. Specifically, polyurethane resins are directly used as fuels or are subjected to treatment for generating steam or fuel gases which are then used as fuels.
The method of the present invention is classified in the chemical recycling technique 2). However, the conventional chemical recycling technique has drawbacks that it requires other compounds such as glycol, amine, and alkali as a decomposing agent, and in addition, it takes long reaction time which renders this technique uneconomical. Due to such drawbacks, there are only a few cases where the conventional chemical recycling technique is actually used for recycling polyurethane resins.
On the other hand, studies have been carried out to develop another chemical recycling technique where polyurethane resins are hydrolyzed into polyol and amine using water as a decomposing agent. For example, Japanese Laid-Open Patent Publication No. 54-70377 discloses a method for decomposing polyurethane in the presence of superheated steam and an alkaline/alkaline earth metal compound at about 300xc2x0 C. or lower and 0.4 to 10 gauge pressure. In the invention disclosed in Japanese Laid-Open Patent Publication No. 54-70377, the inventors have made various studies to find out a method for hydrolyzing polyurethane by superheated steam. However, at a pressure less than 10 gauge pressure, the reaction rate is low and long time is required for reaction. Therefore, they have concluded in the disclosure that the presence of compound which exhibits an activity as catalyst, such as ammonium and alkali, is necessary.
On top of methods for recycling used polyurethane resins, there are also demands for establishing methods for recycling wastes discharged in a chemical plant as by-products. Such wastes, discharged in a chemical plant as distillation residues at a purifying and distilling step of synthesizing a compound having isocyanato groups, almost always contain oligomers such as dimers and trimers of the aimed compound. However, it is impossible to utilize the oligomers. For example, in a chemical plant producing a diisocyanate compound, a diisocyanate compound having high purity is obtained as a finished product at a purifying and distilling step. Although distillation residues generated at the purifying and distilling step contains a diisocyanate compound, i.e., the aimed compound, the distillation residues cannot be recycled and are disposed of as wastes by incineration and the like. This is because the diisocyanate compound cannot be separated from the oligomers thereof or other impurities.
British patent Publications No. 991387 and No. 1047101, U.S. Pat. Nos. 3,225,094 and 4,137,266 respectively disclose a method for hydrolyzing and recycling isocyanate derivatives where isocyanate derivatives are recycled in the form of amine compounds. As all of these methods are batchwise methods, there are disadvantages that large amount of energy is required for raising and lowering temperature and pressure at a time of batch replacement. In addition, in terms of the scale of equipment, there is a limitation on the treating capacity of isocyanate derivatives. Therefore, these methods are not industrially suitable.
Japanese Laid-Open Patent Publication No. 9-151270 discloses a method for recycling tolylenediisocyanate where tolylenediisocyanate is recovered in the form of trylenediamine. However, there is no sufficient disclosure as to the optimum conditions of hydrolysis and of post-processings.
In view of the above, the present invention is aimed at providing an apparatus for and process of efficiently recycling polyurethane resin and wastes discharged at a production line for producing low molecular weight polyisocyanate compounds on an industrial scale using substantially only water with no presence of any compound as a hydrolyzing agent.
According to the present invention, an apparatus for hydrolyzing and recycling polyisocyanate derivatives having at least one isocyanato group and/or a group derived from an isocyanato group as target compounds to be hydrolyzed into raw materials or derivatives thereof for the target compounds, the apparatus includes: a hydrolyzer for bringing only pressurized water in a liquid state at a temperature of 190 to 370xc2x0 C. into contact with the target compounds in the reactor to hydrolyze the target compound: and a post-processor for conducting post-processings such as dewatering, addition, distillation, separation, and liquid separation for a hydrolyzed reaction product discharged from the reactor.